The primary objective of this project is to establish the mechanism of marginal fracture of dental amalgam and to determine and eliminate the factors responsible for this phenomenon. The procedure will consist of determining the nature and distribution of the metallic phases in amalgam using an electron microprobe x-ray analyzer and relating this information to mechanical properties which are known to predict clinical behavior. With this information, present amalgam systems can be improved for clinical usage. BIBLIOGRAPHIC REFERENCES: Mahler, D.B.; Adey, J.D. and Van Eysden, Jan: Quantitative Microprobe Analysis of Amalgam. J. Dent. Res. 54:218 March-April, 1975. Mahler, D.B., Adey, J.D. and Van Eysden, Jan: Microprobe Analysis of a Gold Containing Alloy and Its Amalgam. Submitted for publication August 25, 1975, in the Journal of Dental Research.